How to identify the model/version of a Game Boy cartridge without its sticker?

Sorry if this is late, but I think others might benefit from this information too.

After a closer inspection inside some of my carts the ROM chip has the first two parts of the code and some number, possibly version (usually 0).

For instance, my Mariokart Super Circuit GBA has: AGB-AMKE-USA on the label and, AGB-AMKE-0 on the chip

The 3-letter country code is missing, but the previous letter (at least for GBA games) actually indicates the region (E = America, P = Europe & Australasia, J = Japan, etc). I have a limited number of GB cartridges, but the ones with 4 lettered game codes seem to follow the same system, but the games with only 2 have a different rule. I only have two such games:

DMG-ML-CAN becomes DMG-MLA-1 DMG-YO-UKV becomes DMG-YOX-0

So all I have so far is A = Canada and X = United Kingdom (maybe).

If you have a larger collection you can probably work out the region from that. I hope this is helpful!

EDIT: more info about specific country codes here.

You need to check if there is an engraving on the back of the cartridge or maybe on the very end of the front of it. If it is without a transparent case maybe its beneath it but be careful if you try to take it out.